U.S. patent application number 15/176524 was filed with the patent office on 2017-12-14 for enhanced neutral gear sensor.
This patent application is currently assigned to Allegro MicroSystems, LLC. The applicant listed for this patent is Allegro MicroSystems, LLC. Invention is credited to Andrea Foletto, Andreas P. Friedrich, Cedric Gillet, Yannick Vuillermet.
Application Number | 20170356763 15/176524 |
Document ID | / |
Family ID | 60572476 |
Filed Date | 2017-12-14 |
United States Patent
Application |
20170356763 |
Kind Code |
A1 |
Vuillermet; Yannick ; et
al. |
December 14, 2017 |
ENHANCED NEUTRAL GEAR SENSOR
Abstract
Embodiments provide systems and methods for determining a
position of a gear shift lever of a vehicle. A ferromagnetic target
object having selected characteristics influences a magnetic field
generated by a back bias magnet. A magnetic field sensor includes
magnetic field sensing elements disposed proximate to the target
object. Each magnetic field sensing element generates an electronic
signal in response to sensed magnetic fields. The gear shift lever
moves among a plurality of gears of the vehicle. The magnetic field
sensor selects a set of the magnetic field sensing elements to
determine a magnetic field difference based on a difference of
amplitudes between the electronic signals that is related to a
current position of the gear shift lever. Characteristics of the
target object enable the magnetic field sensor to detect the
position of the gear shift lever. The characteristics include edges
proximate to a perimeter of the target object.
Inventors: |
Vuillermet; Yannick;
(Voglans, FR) ; Gillet; Cedric; (Annecy, FR)
; Foletto; Andrea; (Annecy, FR) ; Friedrich;
Andreas P.; (Metz-Tessy, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Allegro MicroSystems, LLC |
Worcester |
MA |
US |
|
|
Assignee: |
Allegro MicroSystems, LLC
Worcester
MA
|
Family ID: |
60572476 |
Appl. No.: |
15/176524 |
Filed: |
June 8, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16H 59/044 20130101;
G01D 5/147 20130101 |
International
Class: |
G01D 5/14 20060101
G01D005/14; F16H 59/04 20060101 F16H059/04; G01D 5/16 20060101
G01D005/16 |
Claims
1. A system for determining a position of a gear shift lever of a
vehicle, the system comprising: a ferromagnetic target object
having selected characteristics; a back bias magnet configured to
generate a magnetic field influenced by the ferromagnetic target
object; and a magnetic field sensor comprising a plurality of
magnetic field sensing elements disposed proximate to a major
ferromagnetic surface of the ferromagnetic target object, each of
the plurality of magnetic field sensing elements configured to
generate a respective electronic signal in response to respective
sensed magnetic fields; wherein a selected one of the magnetic
field sensor or the ferromagnetic target object is stationary with
respect to the gear shift lever and the other one of the magnetic
field sensor or the ferromagnetic target object is coupled to the
gear shift lever, the gear shift lever configured to move to select
from among a plurality of gears of the vehicle, wherein the
magnetic field sensor is configured to: select a set of the
plurality of magnetic field sensing elements to determine a
magnetic field difference based on a difference of amplitudes
between the electronic signals generated by the selected set of the
plurality of magnetic field sensing elements, wherein the
difference is related to a relative position of the ferromagnetic
target object and the magnetic field sensor; and determine a
current position from a plurality of positions of the gear shift
lever in accordance with the magnetic field difference, the current
position of the gear shift lever corresponding to a gear selected
by the gear shift lever, wherein the selected characteristics of
the ferromagnetic target object are configured to enable the
magnetic field sensor to detect the plurality of positions of the
gear shift lever, and wherein the ferromagnetic object comprises a
perimeter around the major ferromagnetic surface, and wherein one
of the selected characteristics of the ferromagnetic target object
comprises a respective one of a plurality of edges proximate to the
perimeter.
2. The system of claim 1 wherein the selected characteristics of
the ferromagnetic target object comprise a selected shape of the
ferromagnetic target object, the selected shape comprising a
plurality of features, different ones of the plurality of features
corresponding to different ones of the plurality of gears and
disposed at different respective positions on the ferromagnetic
target such that the magnetic field sensor is proximate to
different ones of the plurality of features and distal from other
ones of the plurality of features when the gear shift lever is
moved to different positions, wherein the determined magnetic field
difference has different values when the gear shift lever is in
each position.
3. The system of claim 2, wherein at least one of the plurality of
features comprises a ledge projecting above the major ferromagnetic
surface of the ferromagnetic target object.
4. The system of claim 2, wherein at least one of the plurality of
features comprises a notch removed from the major ferromagnetic
surface of the ferromagnetic target object.
5. The system of claim 2, wherein at least one of the plurality of
features comprises a first radius of a curve of at least a first
section of the ferromagnetic target about an axis.
6. The system of claim 5, wherein at least one of the plurality of
features comprises a second radius of a curve of at least a second
section of the ferromagnetic target about an axis.
7. The system of claim 2, wherein at least one of the plurality of
features comprises a depression into the major ferromagnetic
surface of the ferromagnetic target object.
8. The system of claim 2, wherein the plurality of features is
selected to magnetically interact in different ways with each of
the plurality of magnetic field sensing elements when the gear
shift lever is in each position.
9. The system of claim 2, wherein the at least one magnetic field
sensor has different relative distances to the plurality of
features when the gear shift lever is moved to positions associated
with different respective gears.
10. The system of claim 1, wherein the magnetic field sensor is
configured to select the set of the plurality of magnetic field
sensing elements based upon a relative distance between each of the
plurality of magnetic field sensing elements and the target
object.
11. The system of claim 10, wherein the magnetic field sensor is
configured to select two or more magnetic field sensing elements
that have a greatest combined relative distance from an edge of the
target object.
12. The system of claim 10, wherein the magnetic field sensor is
configured to select two or more magnetic field sensing elements by
weighting each generated electronic signal by a respective weight
coefficient, each respective weight coefficient based upon the
relative distance between each of the plurality of magnetic field
sensing elements and the target object.
13. The system of claim 1, wherein the gear shift lever is
configured to move along one or more translation axes and a
rotation axis.
14. The system of claim 1, wherein the magnetic field sensor is
configured to determine the position of the gear shift lever by
comparing the difference of amplitudes between the electronic
signals generated by each of the selected set of the plurality of
magnetic field sensing elements to one or more threshold
levels.
15. The system of claim 14, wherein the magnetic field sensor is
configured to detect at least three positions of the gear shift
lever.
16. The system of claim 15, wherein: if the difference of
amplitudes reaches a first threshold level, the gear shift lever is
determined to be in a first position; if the difference of
amplitudes reaches a second threshold level but does not reach the
first threshold level, the gear shift lever is determined to be in
a second position; and if the difference of amplitudes does not
reach the second threshold level, the gear shift lever is
determined to be in a third position.
17. The system of claim 16, wherein the second position corresponds
to a neutral position.
18. The system of claim 1, wherein the at least one magnetic field
sensor comprises: an electronic circuit coupled to receive the
first and second sensed magnetic fields, and operable to generate
an output signal indicative of the position of the gear shift
lever.
19. The system of claim 1, wherein the plurality of magnetic field
sensing elements comprises at least one of: planar Hall elements,
vertical Hall elements, fluxgate elements, and magnetoresistance
elements.
20. A method for determining a position of a gear shift lever of a
vehicle, the method comprising: generating a magnetic field by a
back bias magnet influenced by a ferromagnetic target object having
selected characteristics; generating, by each of a plurality of
magnetic field sensing elements of a magnetic field sensor disposed
proximate to a ferromagnetic major surface of the ferromagnetic
target object, an electronic signal in response to sensed magnetic
fields; maintaining a selected one of the magnetic field sensor or
the ferromagnetic target object in a stationary position with
respect to the gear shift lever and coupling the other one of the
magnetic field sensor or the ferromagnetic target object to the
gear shift lever; selecting, by the magnetic field sensor, a set of
the plurality of magnetic field sensing elements and determining a
magnetic field difference based on a difference of amplitudes
between the electronic signals generated by the selected set of the
plurality of magnetic field sensing elements, wherein the
difference is related to a relative position of the ferromagnetic
target object and the magnetic field sensor; and determining, by
the magnetic field sensor, a current position from a plurality of
positions of the gear shift lever in accordance with the magnetic
field difference, the current position of the gear shift lever
corresponding to a gear selected by the gear shift lever, and
detecting, by the magnetic field sensor based upon the selected
characteristics of the ferromagnetic target object, the plurality
of positions of the gear shift lever, wherein the ferromagnetic
object comprises a perimeter around the major ferromagnetic
surface, and wherein one of the selected characteristics of the
ferromagnetic target object comprises a respective one of a
plurality of edges proximate to the perimeter.
21. The method of claim 20, wherein the selected characteristics of
the ferromagnetic target object comprise a selected shape of the
ferromagnetic target object, the selected shape comprising a
plurality of features, different ones of the plurality of features
corresponding to different ones of the plurality of gears and
disposed at different respective positions on the ferromagnetic
target such that the magnetic field sensor is proximate to
different ones of the plurality of features and distal from other
ones of the plurality of features when the gear shift lever is
moved to different positions, wherein the magnetic field difference
has different values when the gear shift lever is in each
position.
22. The method of claim 21, wherein at least one of the plurality
of features comprises a ledge projecting above the major
ferromagnetic surface of the ferromagnetic target object.
23. The method of claim 21, wherein at least one of the plurality
of features comprises a notch removed from the major ferromagnetic
surface of the ferromagnetic target object.
24. The method of claim 21, wherein at least one of the plurality
of features comprises a first radius of a curve of at least a first
section of the ferromagnetic target about an axis.
25. The method of claim 24, wherein at least one of the plurality
of features comprises a second radius of a curve of at least a
second section of the ferromagnetic target about an axis.
26. The method of claim 21, wherein at least one of the plurality
of features comprises a depression into the major ferromagnetic
surface of the ferromagnetic target object.
27. The method of claim 21, further comprising: selecting the
plurality of features to magnetically interact in different ways
with each of the plurality of magnetic field sensing elements when
the gear shift lever is in each position.
28. The method of claim 21, wherein the at least one magnetic field
sensor has different relative distances to the plurality of
features when the gear shift lever is moved to positions associated
with different respective gears.
29. The method of claim 20, wherein the selecting, by the magnetic
field sensor, the set of the plurality of magnetic field sensing
elements, comprises: selecting, by the magnetic field sensor, a set
of the plurality of magnetic field sensing elements based upon a
relative distance between each of the plurality of magnetic field
sensing elements and the target object.
30. The method of claim 29, wherein the selecting, by the magnetic
field sensor, the set comprises: selecting, by the magnetic field
sensor, two or more magnetic field sensing elements by weighting
each generated electronic signal by a respective weight
coefficient, each respective weight coefficient based upon the
relative distance between each of the plurality of magnetic field
sensing elements and the target object.
31. The method of claim 20, further comprising: determining, by the
magnetic field sensor, the position of the gear shift lever by
comparing the difference of amplitudes between the electronic
signals generated by each of the selected set of the plurality of
magnetic field sensing elements to one or more threshold
levels.
32. The method of claim 31, wherein the detecting comprises:
detecting, by the magnetic field sensor, at least three positions
of the gear shift lever.
33. The method of claim 32, further comprising: if the difference
of amplitudes reaches a first threshold level, determining that the
gear shift lever is in a first position; if the difference of
amplitudes reaches a second threshold level but does not reach the
first threshold level, determining that the gear shift lever is in
a second position; and if the difference of amplitudes does not
reach the second threshold level, determining that the gear shift
lever is in a third position.
34. The method of claim 33, wherein the second position corresponds
to a neutral position.
35. The method of claim 20, wherein the at least one magnetic field
sensor comprises an electronic circuit coupled to receive the
sensed magnetic fields, the method further comprising: generating,
by the electronic circuit, an output signal indicative of the
position of the gear shift lever.
36. The method of claim 20, wherein the plurality of magnetic field
sensing elements comprises at least one of: a plurality of planar
Hall elements, a plurality of vertical Hall elements, a plurality
of fluxgate elements, or a plurality of magnetoresistance elements.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] None.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
BACKGROUND
[0003] Magnetic field sensors generally include a magnetic field
sensing element and other electronic components. Magnetic field
sensors provide an electrical signal representative of a magnetic
field sensed by the magnetic field sensing element. Various types
of magnetic field sensing elements are known, including Hall Effect
elements and magnetoresistance elements.
[0004] Magnetic field sensors provide information about a sensed
ferromagnetic object by sensing fluctuations of a sensed magnetic
field. Some magnetic field sensors sense a magnetic field
associated with a magnet as an object moves within a magnetic field
generated by the magnet. In the presence of a moving ferromagnetic
object, the magnetic field signal sensed by the magnetic field
sensor varies in accordance with a shape or profile of the moving
ferromagnetic object (a "target object").
[0005] In automotive applications, a typical magnetic field sensor
might determine the position of a target object, for example, the
position of a gear shift lever in an automotive transmission. Such
systems might beneficially sense a neutral position of a gear shift
lever used in a vehicle transmission. For example, stop-start
systems reduce fuel consumption and emissions by turning off a
vehicle's engine when the vehicle is stopped. Using a neutral gear
sensor to sense the neutral position, an engine control unit (ECU)
might turn off the engine to reduce fuel consumption when the
vehicle is stopped, for example, if a gear shift level is in a
neutral position and the clutch is engaged (e.g., the clutch pedal
is not pushed). Thereafter, when the clutch is disengaged (e.g.,
the clutch pedal is pushed to select a gear), the engine control
unit starts the engine.
[0006] Some current neutral gear sensors employ a single Hall
plate, a zero Gauss magnet (i.e., a magnet with an area proximate
to the magnet at which the magnetic field is zero) and a
ferromagnetic target object. The target object moves in a rotation
and a translation with respect to the neutral gear sensor. The air
gap between the target and the sensor typically is unchanged along
the translation, but varies with the target rotation (e.g., the air
gap between the ferromagnetic target object and the sensor changes
with the rotation of the target object). This air gap variation
corresponds to a variation of the magnetic field measured by the
sensor, which can, in turn, be used to determine the gear shift
lever position.
[0007] However, current neutral gear sensors can be sensitive to
external magnetic fields and magnetic field perturbations,
decreasing measurement accuracy. Further, since the measurement is
unipolar (e.g., the sensed magnetic field is in the same direction
regardless of target position), the measurement has high
sensitivity to air gap variation (e.g., due to mounting and
orientation in different vehicles, manufacturing tolerances, etc.).
Conventional systems can also be sensitive to magnetic field
strength drift over temperature variations. Consequently, some
magnetic field sensors employ continuous time calibration to
maintain accurate detection of the neutral position, but such
calibration increases system cost and complexity and, in some
instances, eliminates the ability to correctly detect additional
gear shift lever position(s) (e.g., reverse, etc.). Further, zero
Gauss magnets, can increase the overall system cost.
[0008] Therefore, it is desirable to provide a system that senses
the neutral position as well as other positions of the gear shift
lever without requiring continuous calibration and expensive
magnetic components.
SUMMARY
[0009] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key or essential features or combinations of the claimed subject
matter, nor is it intended to be used to limit the scope of the
claimed subject matter.
[0010] In one aspect, a system for determining a position of a gear
shift lever of a vehicle is provided. A ferromagnetic target object
having selected characteristics influences a magnetic field
generated by a back bias magnet. A magnetic field sensor includes a
plurality of magnetic field sensing elements disposed proximate to
a major ferromagnetic surface of the ferromagnetic target object.
Each of the magnetic field sensing elements generate a respective
electronic signal in response to respective sensed magnetic fields.
A selected one of the magnetic field sensor or the ferromagnetic
target object is stationary with respect to the gear shift lever
and the other is coupled to the gear shift lever. The gear shift
lever moves to select from among a plurality of gears of the
vehicle. The magnetic field sensor selects a set of the plurality
of magnetic field sensing elements to determine a magnetic field
difference based on a difference of amplitudes between the
electronic signals generated by the selected set of the plurality
of magnetic field sensing elements. The difference is related to a
relative position of the ferromagnetic target object and the
magnetic field sensor. A current position of the gear shift lever
is determined based upon the magnetic field difference. The
selected characteristics of the ferromagnetic target object enable
the magnetic field sensor to detect the plurality of positions of
the gear shift lever. The ferromagnetic object includes a perimeter
around the major ferromagnetic surface, and one of the selected
characteristics of the ferromagnetic target object includes a
respective one of a plurality of edges proximate to the
perimeter.
[0011] In an embodiment, the selected characteristics of the
ferromagnetic target object include a selected shape of the
ferromagnetic target object. The selected shape includes a
plurality of features, different ones of the plurality of features
corresponding to different ones of the plurality of gears and
disposed at different respective positions on the ferromagnetic
target such that the magnetic field sensor is proximate to
different ones of the plurality of features and distal from other
ones of the plurality of features when the gear shift lever is in
each to different positions. The sensed magnetic fields have
different values when the gear shift lever is in each position. In
an embodiment, at least one of the features includes a ledge
projecting above the major ferromagnetic surface of the
ferromagnetic target object. In an embodiment, at least one of the
features includes a notch removed from a major surface of the
ferromagnetic target object. In an embodiment, at least one of the
features includes a first radius of a curve of at least a first
section of the ferromagnetic target about an axis. In an
embodiment, at least one of the plurality of features includes a
second radius of a curve of at least a second section of the
ferromagnetic target about an axis. In an embodiment, at least one
of the plurality of features includes a depression into the major
ferromagnetic surface of the ferromagnetic target object. In an
embodiment, the features are selected to magnetically interact in
different ways with each of the plurality of magnetic field sensing
elements when the gear shift lever is in each position. In an
embodiment, the at least one magnetic field sensor has different
relative distances to the plurality of features when the gear shift
lever is moved to positions associated with different respective
gears.
[0012] In an embodiment, the magnetic field sensor selects the set
of the plurality of magnetic field sensing elements based upon a
relative distance between each of the plurality of magnetic field
sensing elements and the target object. In an embodiment, the
magnetic field sensor selects two or more magnetic field sensing
elements that have a greatest combined relative distance from an
edge of the target object. In an embodiment, the magnetic field
sensor selects two or more magnetic field sensing elements by
weighting each generated electronic signal by a respective weight
coefficient, each respective weight coefficient based upon the
relative distance between each of the plurality of magnetic field
sensing elements and the target object.
[0013] In an embodiment, the gear shift lever moves along one or
more translation axes and a rotation axis. In an embodiment, the
magnetic field sensor determines the position of the gear shift
lever by comparing the difference of amplitudes between the
electronic signals generated by each of the selected set of the
plurality of magnetic field sensing elements to one or more
threshold levels. In an embodiment, the magnetic field sensor
detects at least three positions of the gear shift lever. In an
embodiment, if the difference of amplitudes reaches a first
threshold level, the gear shift lever is determined to be in a
first position. If the difference of amplitudes reaches a second
threshold level but does not reach the first threshold level, the
gear shift lever is determined to be in a second position. If the
difference of amplitudes does not reach the second threshold level,
the gear shift lever is determined to be in a third position. In an
embodiment, the second position corresponds to a neutral
position.
[0014] In an embodiment, the at least one magnetic field sensor
includes an electronic circuit coupled to receive the first and
second sensed magnetic fields, and operable to generate an output
signal indicative of the position of the gear shift lever.
[0015] In an embodiment, the plurality of magnetic field sensing
elements includes at least one of: planar Hall elements, vertical
Hall elements, fluxgate elements, and magnetoresistance
elements.
[0016] In another aspect, a method for determining a position of a
gear shift lever of a vehicle is provided. A magnetic field is
generated by a back bias magnet influenced by a ferromagnetic
target object having selected characteristics. A plurality of
magnetic field sensing elements of a magnetic field sensor is
disposed proximate to a major ferromagnetic surface of the
ferromagnetic target object. Each of the magnetic field sensing
elements generate an electronic signal in response to sensed
magnetic fields. A selected one of the magnetic field sensor or the
ferromagnetic target object is maintained in a stationary position
with respect to the gear shift lever. The other one of the magnetic
field sensor or the ferromagnetic target object is coupled to the
gear shift lever. The magnetic field sensor selects a subset of the
plurality of magnetic field sensing elements and determines a
magnetic field difference based on a difference of amplitudes
between the electronic signals generated by the selected subset of
the plurality of magnetic field sensing elements. The difference is
related to a relative position of the ferromagnetic target object
and the magnetic field sensor. The magnetic field sensor determines
a current position from a plurality of positions of the gear shift
lever in accordance with the magnetic field difference. The current
position of the gear shift lever corresponds to a gear selected by
the gear shift lever. The magnetic field sensor determines, based
upon the selected characteristics of the ferromagnetic target
object, the plurality of positions of the gear shift lever. The
ferromagnetic object includes a perimeter around the major
ferromagnetic surface, and one of the selected characteristics of
the ferromagnetic target object includes a respective one of a
plurality of edges proximate to the perimeter.
[0017] In an embodiment, the selected characteristics of the
ferromagnetic target object include a selected shape of the
ferromagnetic target object. The selected shape includes a
plurality of features, different ones of the plurality of features
corresponding to different ones of the plurality of gears and
disposed at different respective positions on the ferromagnetic
target such that the magnetic field sensor is proximate to
different ones of the plurality of features and distal from other
ones of the plurality of features when the gear shift lever is
moved to different positions. The sensed magnetic fields have
different values when the gear shift lever is in each position. In
an embodiment, at least one of the features includes a ledge
projecting above the major ferromagnetic surface of the
ferromagnetic target object. In an embodiment, at least one of the
features includes a notch removed from the major ferromagnetic
surface of the ferromagnetic target object. In an embodiment, at
least one of the features includes a first radius of a curve of at
least a first section of the ferromagnetic target about an axis. In
an embodiment, at least one of the plurality of features includes a
second radius of a curve of at least a second section of the
ferromagnetic target about an axis. In an embodiment, at least one
of the plurality of features includes a depression into the major
ferromagnetic surface of the ferromagnetic target object. In an
embodiment, the features are selected to magnetically interact in
different ways with each of the plurality of magnetic field sensing
elements when the gear shift lever is in each position. In an
embodiment, the at least one magnetic field sensor has different
relative distances to the plurality of features when the gear shift
lever is moved to positions associated with different respective
gears.
[0018] In an embodiment, the magnetic field sensor selects a set of
the plurality of magnetic field sensing elements based upon a
relative distance between each of the plurality of magnetic field
sensing elements and the target object. In an embodiment, the
magnetic field sensor selects two or more magnetic field sensing
elements that have a greatest combined relative distance from an
edge of the target object. In an embodiment, the magnetic field
sensor selects two or more magnetic field sensing elements by
weighting each generated electronic signal by a respective weight
coefficient, each respective weight coefficient based upon the
relative distance between each of the plurality of magnetic field
sensing elements and the target object.
[0019] In an embodiment, the magnetic field sensor determines the
position of the gear shift lever by comparing the difference of
amplitudes between the electronic signals generated by each of the
selected set of the plurality of magnetic field sensing elements to
one or more threshold levels. In an embodiment, the magnetic field
sensor detects at least three positions of the gear shift lever. In
an embodiment, if the difference of amplitudes reaches a first
threshold level, the gear shift lever is determined to be in a
first position. If the difference of amplitudes reaches a second
threshold level but does not reach the first threshold level, the
gear shift lever is determined to be in a second position. If the
difference of amplitudes does not reach the second threshold level,
the gear shift lever is determined to be in a third position. In an
embodiment, the second position corresponds to a neutral
position.
[0020] In an embodiment, the at least one magnetic field sensor
includes an electronic circuit coupled to receive the first and
second sensed magnetic fields, and operable to generate an output
signal indicative of the position of the gear shift lever.
[0021] In an embodiment, the plurality of magnetic field sensing
elements includes at least one of: planar Hall elements, vertical
Hall elements, fluxgate elements, and magnetoresistance
elements.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0022] Other aspects, features, and advantages of the described
embodiments will become more fully apparent from the following
detailed description, the appended claims, and the accompanying
drawings in which like reference numerals identify similar or
identical elements. Reference numerals that are introduced in the
specification in association with a drawing figure might be
repeated in one or more subsequent figures without additional
description in the specification in order to provide context for
other features.
[0023] FIG. 1 is a block diagram showing an illustrative gearshift
lever position sensing system having a gear shift lever, a magnetic
field sensor, and a target object;
[0024] FIG. 2 is a diagram showing an isometric view of a gearshift
lever position sensing system having an illustrative target object
disposed proximate to a magnetic field sensor with three magnetic
field sensing elements;
[0025] FIG. 3 is a diagram showing a top view of the gearshift
lever position sensing system and target object of FIG. 2;
[0026] FIG. 4 is a diagram showing a plot of differential signals
generated by the magnetic field sensor of FIGS. 1-3 versus relative
motion of the gear shift lever and the target object along the
lines shown in FIG. 3;
[0027] FIG. 5 is a diagram showing a top view of an illustrative
arrangement of three magnetic field sensing elements with respect
to a back bias magnet and an edge of an illustrative target object
of FIG. 3;
[0028] FIG. 6 is a diagram showing a top view of another
illustrative arrangement of three magnetic field sensing elements
with respect to a magnet and an edge of an illustrative target
object of FIG. 3;
[0029] FIG. 7 is a diagram showing an isometric view of another
illustrative target object having a ridge disposed proximate to a
magnetic field sensor with three magnetic field sensing
elements;
[0030] FIG. 8 is a diagram showing an isometric view of another
illustrative target object having a notched ridge, the target
object disposed proximate to a magnetic field sensor with three
magnetic field sensing elements;
[0031] FIG. 9 is a diagram showing an isometric view of another
illustrative curved target object having a ridge and a notch, the
target object disposed proximate to a magnetic field sensor with
three magnetic field sensing elements;
[0032] FIG. 10 is a diagram showing an isometric view of another
illustrative curved target object having sections with different
radii, the target object disposed proximate to a magnetic field
sensor with three magnetic field sensing elements;
[0033] FIG. 11 is a diagram showing a plot of differential signals
generated by the magnetic field sensor of FIG. 10 versus relative
motion of the gear shift lever and the target object along the
lines shown in FIG. 3; and
[0034] FIG. 12 is a flow diagram showing an illustrative technique
for operating the magnetic field sensor of FIG. 1.
DETAILED DESCRIPTION
[0035] As used herein, the term "magnetic field sensing element" is
used to describe a variety of electronic elements that can sense a
magnetic field. The magnetic field sensing element can be, but is
not limited to, a Hall effect element, a fluxgate element, a
magnetoresistance element, or a magnetotransistor. There are
different types of Hall effect elements, for example, a planar Hall
element, a vertical Hall element, and a Circular Vertical Hall
(CVH) element. There are also different types of magnetoresistance
elements, for example, a semiconductor magnetoresistance element
such as Indium Antimonide (InSb), a giant magnetoresistance (GMR)
element, for example, a spin valve, an anisotropic
magnetoresistance element (AMR), a tunneling magnetoresistance
(TMR) element, and a magnetic tunnel junction (MTJ). The magnetic
field sensing element might be a single element or, alternatively,
might include two or more magnetic field sensing elements arranged
in various configurations, e.g., a half bridge or full (Wheatstone)
bridge. Depending on the device type and other application
requirements, the magnetic field sensing element might be a device
made of a type IV semiconductor material such as Silicon (Si) or
Germanium (Ge), or a type III-V semiconductor material like
Gallium-Arsenide (GaAs) or an Indium compound, e.g.,
Indium-Antimonide (InSb).
[0036] Some of the above-described magnetic field sensing elements
tend to have an axis of maximum sensitivity parallel to a substrate
that supports the magnetic field sensing element, and others of the
above-described magnetic field sensing elements tend to have an
axis of maximum sensitivity perpendicular to a substrate that
supports the magnetic field sensing element. In particular, planar
Hall elements tend to have axes of sensitivity perpendicular to a
substrate, while metal based or metallic magnetoresistance elements
(e.g., GMR, TMR, AMR) and vertical Hall elements tend to have axes
of sensitivity parallel to a substrate.
[0037] As used herein, the term "magnetic field sensor" is used to
describe a circuit that uses a magnetic field sensing element,
generally in combination with other circuits. Magnetic field
sensors are used in a variety of applications, including, but not
limited to, an angle sensor that senses an angle of a direction of
a magnetic field, a current sensor that senses a magnetic field
generated by a current carried by a current-carrying conductor, a
magnetic switch that senses the proximity of a ferromagnetic
object, a rotation detector that senses passing ferromagnetic
articles, for example, magnetic domains of a ring magnet or a
ferromagnetic target (e.g., gear teeth) where the magnetic field
sensor is used in combination with a back-bias or other magnet, and
a magnetic field sensor that senses a magnetic field density of a
magnetic field.
[0038] As used herein below, the term "ferromagnetic target
object," or simply "target object" is used to describe a mechanical
structure, movement of which is sensed by a magnetic field
sensor.
[0039] As used herein, the term "movement axis" is used to describe
an axis along which a target object can move linearly relative to a
location of a magnetic field sensor. The term "movement axis" is
also used to describe an axis along which the magnetic field sensor
can move linearly relative of a location of a ferromagnetic target
object. In some arrangements, both the ferromagnetic target object
and the magnetic field sensor can move relative to each other along
respective movement axes.
[0040] As used herein, the term "movement line" is used to describe
a line, which might be straight or curved, along which a target
object can move relative to a location of a magnetic field sensor.
The term "movement line" is also used to describe a line, straight
or curved, along which the magnetic field sensor can move relative
of a location of a ferromagnetic target object. In some
arrangements, both the ferromagnetic target object and the magnetic
field sensor can move relative to each other along respective
movement lines.
[0041] It should be understood that a movement line can be a
movement axis and a movement axis can be a movement line. However,
a movement line can be curved while a movement axis is
straight.
[0042] As used herein, the term "rotation axis" is used to describe
an axis upon which a target object can rotate or spin. In some
arrangements, the movement axis and the rotation axis are parallel
to each other. In some arrangements, the movement axis and the
rotation axis are the same axis.
[0043] Described embodiments provide systems and methods for
determining a position of a gear shift lever of a vehicle. In
particular, described embodiments can be used to determine at least
three gear positions, namely, neutral, reverse, and a grouping of
forward gears. A ferromagnetic target object (e.g., 103 of FIG. 1)
having selected characteristics influences a magnetic field
generated by a back bias magnet (e.g., 104). A magnetic field
sensor (e.g., 102) includes a plurality of magnetic field sensing
elements (e.g., 106) disposed proximate to a major ferromagnetic
surface (e.g., 204 of FIG. 2, 704 of FIG. 7, 804 of FIG. 8, 904 of
FIG. 9 or 1004 of FIG. 10) of the ferromagnetic target object. Each
of the magnetic field sensing elements generate a respective
electronic signal (e.g., 122) in response to respective sensed
magnetic fields corresponding to the magnetic field. A selected one
of the magnetic field sensor or the ferromagnetic target object is
stationary with respect to the gear shift lever (e.g., 101) and the
other is coupled to the gear shift lever. The gear shift lever
moves to select from among a plurality of gears of the vehicle. The
magnetic field sensor selects a set of the plurality of magnetic
field sensing elements to determine a difference of amplitudes
between the electronic signals generated by the selected set of the
plurality of magnetic field sensing elements. The difference is
related to a relative position of the ferromagnetic target object
and the magnetic field sensor. A current position of the gear shift
lever is determined based upon the difference. The selected
characteristics of the ferromagnetic target object enable the
magnetic field sensor to detect the plurality of positions of the
gear shift lever. The ferromagnetic object includes a perimeter
(e.g., 205 of FIG. 2, 705 of FIG. 7, 805 of FIG. 8, 905 of FIG. 9
or 1005 of FIG. 10) around the major ferromagnetic surface, and one
of the selected characteristics of the ferromagnetic target object
includes a respective one of a plurality of edges (e.g., 206 of
FIGS. 2, 706a and 706b of FIGS. 7, 806 and 812 of FIGS. 8, 906 and
912 of FIG. 9 or 1006 and 1012 of FIG. 10) proximate to the
perimeter.
[0044] Referring to FIG. 1, a gear shift sensing system 100 is
associated with a gear shift lever 101 that may be used in any type
of vehicle, including, but not limited to automobiles, trucks, and
boats. Gear shift sensing system 100 includes magnetic field sensor
102 that may include a plurality of magnetic field sensing
elements, shown to be three magnetic field sensing elements labeled
1, 2 and 3, which are shown collectively as magnetic field sensing
elements 106. Magnet 104 may be disposed within magnetic field
sensor 102 or otherwise can be proximate to the magnetic field
sensor 102. Magnet 104 provides a magnetic field to back bias
magnetic field sensing elements 106 in a "back-biased" arrangement.
In some embodiments, magnetic field sensor 102 may be implemented
as an integrated circuit.
[0045] In some embodiments, magnetic field sensing elements 106 may
be Hall effect elements, and are disposed in a plane proximate to
ferromagnetic target object 103. In some embodiments, magnet 104 is
disposed on a distal side of magnetic field sensing elements 106
from ferromagnetic target 103. Ferromagnetic objects passing near
to magnet 104 will tend to alter the magnetic field surrounding
magnet 104. These alterations can be sensed by magnetic field
sensing elements 106, each of which generates magnetic field
signals in response to a sensed magnetic field. The magnetic field
signals are shown collectively as magnetic field signals 106a.
Multiplexer 108 may receive magnetic field signals 106a and
generate a multiplexed magnetic field signal 108a having a series
sequence of magnetic field signals 106a received by the multiplexer
108.
[0046] In some embodiments, magnetic field sensor 102 may include
summing node 110 to receive multiplexed magnetic field signal 108a
and to receive a correction signal 112. For example, correction
signal 112 might be operable to reduce a direct current (DC) offset
of multiplexed magnetic field signal 108a. Summing node 110
generates corrected signal 110a. Amplifier 114 receives corrected
signal 110a and calibration signal 116, and generates calibrated
signal 114a. For example, calibration signal 116 might be operable
to calibrate gain of amplifier 114, for example, to compensate for
temperature variations of gear shift sensing system 100.
Analog-to-digital converter (ADC) 118 receives calibrated signal
114a and generates calibrated digital signal 118a.
[0047] Digital demultiplexer 120 receives calibrated digital signal
118a and may generate one or more calibrated digital magnetic field
signals, shown collectively as calibrated digital magnetic field
signals 122. For example, digital demultiplexer 120 may generate a
calibrated digital magnetic field signal corresponding to each
magnetic field sensing element 106. Thus, for the embodiment shown
in FIG. 1, digital demultiplexer 120 generates three calibrated
digital magnetic field signals, one corresponding to each magnetic
field sensing element 106, labeled Hall_1, Hall_2 and Hall_3
(although magnetic field sensing elements 106 are not limited only
to Hall elements).
[0048] Calibrated digital magnetic field signals 122 are provided
to processing system 124. Processing system 124 can include a
plurality of differencing processors, memory or other circuitry. In
some embodiments, processing system 124 may include Hall processing
system 126, memory 128, input/output (I/O) processing system 130,
and calibration and/or temperature compensation system 134.
Calibration and/or temperature compensation system 134 may generate
correction signal 112 and calibration signal 116, for example based
on temperature compensation signal 132 provided to calibration
and/or temperature compensation system 134. Hall processing system
126 may process calibrated digital magnetic field signals 122 to
determine a position of, and therefore a gear (e.g., at least
neutral, reverse, and any of the forward gears taken as a
collective group) selected by, gear shift lever 101. In some
embodiments, Hall processing system 126 may compare differences of
two or more of calibrated digital magnetic field signals 122, e.g.,
differences of two or more pairs of calibrated digital magnetic
field signals 122. The difference or differences may then be
compared with one or more predetermined values stored in memory 128
to generate a selected gear signal (not shown), which is indicative
of the gear selected by gear shift lever 101.
[0049] The selected gear signal may be provided to I/O processing
system 130, which generates output signal 136. Output signal 136
may represent the selected gear (e.g., include data related to the
selected gear signal), but may be generated in one of a variety of
output signal formats. For example, output signal 136 may be
generated as a serial or parallel digital signal, a pulse width
modulated (PWM) signal or an analog signal. In other embodiments,
output signal 136 may be generated in accordance with various
signal formats, for example, a Single Edge Nibble Transmission
(SENT) format, a Serial Peripheral Interface (SPI) format, a Local
Interconnect Network (LIN) format, a CAN (Controller Area Network)
format, an Inter-Integrated Circuit (I2C) format, or other similar
signal formats. For example, in automotive applications, output
signal 136 might be communicated to an Electronic/Engine Control
Unit (ECU), Engine Control Module (ECM) or similar controller of an
automotive system.
[0050] In some embodiments, ferromagnetic target object 103 may be
coupled to gear shift lever 101 and magnetic field sensor 102 is
coupled to a structure (not shown) that is stationary relative to
gear shift lever 101 as gear shift lever 101 is moved (e.g.,
shifted) between gears. In other embodiments, magnetic field sensor
102 may be coupled to gear shift lever 101 and ferromagnetic target
103 is coupled to a structure (not shown) that is stationary
relative to gear shift lever 101 as gear shift lever 101 is moved
(e.g., shifted) between gears. In either arrangement, magnetic
field sensor 102 is responsive to a position of ferromagnetic
target 103 relative to magnetic field sensor 102, and therefore, to
a position of gear shift lever 101.
[0051] As described herein, ferromagnetic target 103 has a shape
(e.g., a perimeter shape) and features (i.e., characteristics) that
allow magnetic field sensor 102 to identify the position of gear
shift lever 101 in one or more gear positions associated with
different gears of the vehicle. In one embodiment, three (3)
specific positions (e.g., gears) are detected using shapes and
features of ferromagnetic target 103 and a back bias differential
magnetic field sensor (e.g., 102). In described embodiments, to
detect at least three specific positions, magnetic field sensor 102
can employ three magnetic field sensing elements 106 disposed at
different locations relative to ferromagnetic target 103. Thus,
described embodiments may detect neutral, reverse and forward gears
collectively (or at least one specific gear), while being
substantially insensitive to external perturbations of the magnetic
fields, and being independent of movement of magnetic field sensor
102 relative to ferromagnetic target 103 around the Z axis of FIG.
2. Described embodiments employ a differential measurement of the
magnetic field, instead of a single direct measurement, to generate
an output that is less sensitive to changes in an air gap distance
between ferromagnetic target 103 and magnetic field sensor 102.
[0052] Referring to FIG. 2, an illustrative structure of
ferromagnetic target object 103 of FIG. 1 is shown as ferromagnetic
target object 202. Illustrative ferromagnetic target object 202 has
a shape operable to allow magnetic field sensor 208 to detect three
relative positions of ferromagnetic target object 202. As shown,
magnetic field sensor 208 may include three magnetic field sensing
elements, 210a, 210b and 210c. Magnetic field sensor 208 may also
include back bias magnet 213. In some embodiments, back bias magnet
213 is magnetized along a Z axis as labeled in FIG. 2. In described
embodiments, back bias magnet 213 is a standard magnet, such as a
parallelepiped magnet, and is not a zero Gauss magnet. In some
embodiments, magnet 213 can have a square shape, a rectangular
shape, or a cylindrical shape.
[0053] Magnetic field sensing elements 210a, 210b and 210c are
disposed in an X-Y plane as labeled in FIG. 2. In some embodiments,
magnetic field sensing elements 210a, 210b and 210c are sensitive
to magnetic fields along the Z axis. In an embodiment,
ferromagnetic target object 202 moves along X and Y axes (e.g., two
translations) relative to magnetic field sensor 208. In another
embodiment, magnetic field sensor 208 moves along the X and Y axes
(e.g., two translations) relative to ferromagnetic target object
202. Ledge 206 is disposed on major surface 204 of ferromagnetic
target object 202 and has a surface in the X-Y plane. For example,
as shown in FIG. 2, ledge 206 extends along part of a length along
the X axis of ferromagnetic target object 202. In an embodiment,
ledge 206 does not extend along the full length of ferromagnetic
target object 202 along the X axis.
[0054] Referring to FIG. 3, in which like elements of FIG. 2 are
shown having like reference designations, a top view of
ferromagnetic target object 202 and magnetic field sensor 208 in
gear shift system 300 is shown. FIG. 3 shows that illustrative gear
shift system 300 may have eight gears: G1, G2, G3, G4, G5, G6,
Reverse (R) and Neutral (N), although other systems may have fewer
than eight or more than eight gears. The neutral position is
referred to herein as a gear, although the neutral position is
sometimes considered to represent an absence of a gear or not being
in gear. Dotted line 302 indicates illustrative movement (e.g.,
translation) of a manual vehicle gear shift (e.g., gear shift lever
101 of FIG. 1) to select associated gears of a vehicle. As would be
understood, other gear arrangements may be employed.
[0055] Ferromagnetic target object 202 is disposed with respect to
the movement (translation) of gear shift lever 101. For the
illustrative embodiment shown in FIG. 2, magnetic field sensor 208
may be mounted to gear shift lever 101 such that magnetic field
sensor 208 moves, with the gear shift lever 101, relative to
ferromagnetic target object 103. As magnetic field sensor 208 moves
along dotted line 302, magnetic fields sensed by magnetic field
sensing elements 210a, 210b and 210c may change. In some
embodiments, a differential field signal might be determined based
on a difference between selected ones of the magnetic fields sensed
by magnetic field sensing elements 210a, 210b and 210c (e.g., by
determining a difference between selected ones of magnetic field
signals 122 of FIG. 1).
[0056] It should be appreciated that, at position R (reverse),
magnetic field sensor 208 can overlap a perimeter edge of
ferromagnetic target object 202, at position N (neutral), magnetic
field sensor 208 does not overlaps a perimeter edge of
ferromagnetic target object 202, at a set of positions G2, G4, G6
(forward gears 2, 4, 6), magnetic field sensor 208 can overlap a
different perimeter edge of ferromagnetic target object 202, and at
a set of positions G1, G3, G5 (forward gears 1, 3, 5), magnetic
field sensor 208 can overlap ledge 206. Magnetic field sensor 208
is operable to detect and identify reverse, neutral, and forward
gears.
[0057] Referring to FIG. 4, plot 400 has a horizontal axis with a
scale in units of distance in the Y axis of figures herein, and a
vertical axis with a scale in units of differential signal in
arbitrary units. Differential signal curves 402 and 404, represent
differential magnetic field signals associated with magnetic field
sensing elements 210b, 210c of FIG. 2 aligned along the Y axis of
FIG. 2 for relative position of magnetic field sensor 208 and
ferromagnetic target object 204 along line L1 of FIG. 3 (curve 404)
and line L2 of FIG. 3 (curve 402), which are both parallel to the Y
axis. Plot 400 shows the magnitude of the differential signal on
the vertical axis, versus position along the Y axis as in FIG. 3.
The differential magnetic field is increasingly positive or
negative (e.g., at large translation of gear shift lever 101).
[0058] It should be appreciated that the right hand side of curve
404 is indicative of the position of the reverse gear (R), for
which magnetic field sensor 208 of FIG. 2 is proximate to a right
hand perimeter of ferromagnetic target object 204. It should be
also appreciated that the right hand side of curve 402 is
indicative of the position of the gear G3 (also G1 and G5), for
which magnetic field sensor 208 of FIG. 2 is also proximate to a
right hand perimeter of ferromagnetic target object 204, but
magnetic field sensor 208 is also over ledge 206. Thus, the right
hand side of curve 404 is negative while the right hand side of
curve 402 is positive.
[0059] Described embodiments may employ a plurality of thresholds
to determine the position (e.g., selected gear) of gear shift lever
101. As shown in FIG. 4, some embodiments may employ two
thresholds, T1 and T2, to determine 3 positions (e.g., gears). For
example, when the differential magnetic field signal, dH, is
greater than threshold T1, gear shift lever 101 may be determined
to be in a position, S1, associated with a first given gear. For
example, position S1 may correspond to one or more forward gears.
When the differential magnetic field signal, dH, is between
thresholds T1 and T2, gear shift lever 101 may be determined to be
in a position, S2, associated with a second given gear over a
position range from Y1 to Y2. For example, position S2 may
correspond to neutral. When the differential magnetic field signal,
dH, is less than threshold T2, gear shift lever 101 may be
determined to be in a position, S3, associated with a third given
gear. For example, position S3 may correspond to reverse.
[0060] In order to be independent of the orientation of magnetic
field sensing elements 210 around the Z axis with respect to
ferromagnetic target object 202, described embodiments employ more
than two magnetic field sensing elements.
[0061] Referring to FIGS. 5 and 6, illustrative arrangement 500 of
magnetic field sensing elements M1, M2 and M3 is shown. As shown,
magnetic field sensing elements M1, M2 and M3 may be disposed in a
circular arrangement relative to each other (e.g., on a radius, D).
Magnetic field sensing elements M1, M2 and M3 may be equidistant
from each other. FIG. 5 depicts a first illustrative orientation of
magnetic field sensing elements M1, M2 and M3 relative to
ferromagnetic target feature 504 (e.g., such as ledge 206, etc.). A
magnet 502 can be disposed over the magnetic field sensing elements
M1, M2, M3. FIG. 6 shows a second illustrative orientation of
magnetic field sensing elements M1, M2 and M3 relative to
ferromagnetic target feature 504, which may be the ferromagnetic
target, or a feature of the ferromagnetic target (e.g., such as
ledge 206, etc.).
[0062] In the orientation shown in FIG. 5, magnetic field sensor M3
is disposed over ferromagnetic target feature 504, while magnetic
field sensors M1 and M2 are not disposed over ferromagnetic target
feature 504. As shown in FIG. 5, magnetic field sensing element M1
is a distance D.sub.1 away from ferromagnetic target feature 504
and magnetic field sensing element M2 is a distance D.sub.2 away
from ferromagnetic target feature 504. As shown in the illustrative
position of FIG. 5, distances D.sub.1 and D.sub.2 may be
approximately equal. In this orientation, described embodiments
desirably employ the magnetic field signals (e.g., magnetic field
signals 122) generated by magnetic field sensing elements M1 and M3
(or M2 and M3) to generate the differential magnetic field signal,
dH. For example, dH=M3-M2, or dH=M3-M1, or both.
[0063] In the orientation shown in FIG. 6, magnetic field sensor M3
is disposed over ferromagnetic target feature 504, magnetic field
sensor M2 is not disposed over ferromagnetic target feature 504,
and magnetic field sensor M1 is partially disposed over
ferromagnetic target feature 504 (e.g., distance D.sub.1 is almost
zero). As shown in FIG. 6, magnetic field sensing element M2 is a
distance D.sub.2 away from ferromagnetic target feature 504. As
shown in the illustrative position of FIG. 6, distance D.sub.2 may
be greater than distance D.sub.1. In this orientation, described
embodiments desirably employ the magnetic field signals (e.g.,
magnetic field signals 122) generated by magnetic field sensing
elements M2 and M3 to generate the differential magnetic field
signal, dH. For example, dH=M3-M2.
[0064] As shown in FIGS. 5 and 6, by employing three magnetic field
sensing elements 210a, 210b and 210c, the spacing achieved between
the magnetic field sensing elements employed to generate the
differential magnetic field signal, dH, may be approximately 1.5D,
where D is the radius of a circle about which the magnetic field
sensing elements are disposed. In described embodiments,
peak-to-peak differential field variation may be improved by
increasing D (e.g., increasing the radius of the circle about which
the magnetic field sensing elements are disposed), limited by a die
size of the magnetic field sensor (e.g., 102).
[0065] Some described embodiments may generate the differential
magnetic field signal, dH, as the difference between the magnetic
field signals (e.g., 122) generated by the two magnetic field
sensing elements with the largest spacing relative to ferromagnetic
target feature 504.
[0066] Another embodiment may employ a weighted sum of the magnetic
field signals (e.g., 122) to generated the differential magnetic
field signal, dH. For example, some embodiments may add the signals
by:
dH = i = 1 n .alpha. i M i ( 1 ) ##EQU00001##
where n is the total number of magnetic field sensing elements and
.alpha..sub.i are n weighting coefficients associated with the n
magnetic field sensing elements. In an embodiment, weighting
coefficients .alpha..sub.i are between -1 and 1, where:
i = 1 n .alpha. i = 0 ( 2 ) ##EQU00002##
such that external magnetic fields (e.g., perturbations and
glitches) are rejected. In illustrative embodiments shown in FIGS.
5 and 6 having three magnetic field sensing elements (e.g., n=3),
one might employ weighting coefficients .alpha..sub.1=0,
.alpha..sub.2=-1, and .alpha..sub.3=1. Another embodiment having
three magnetic field sensing elements (e.g., n=3) might employ
weighting coefficients .alpha..sub.1=-0.5, .alpha.2=-0.5, and
.alpha..sub.3=1 (e.g., dH=M3-(M1+M2)/2).
[0067] Referring to FIGS. 7 and 8, other illustrative embodiments
may employ ferromagnetic target objects as shown in FIGS. 7 and 8,
in which magnetic field sensors 708, 808 with magnet 713, 813 and
magnetic field sensing elements 710a, 710b, 710c, 810a, 810b, 810c
can be the same as or similar to magnetic field sensor 208 with
magnet 213 and magnetic field sensing elements 210a, 210b, 210c of
FIG. 2. For example, in FIG. 7, ferromagnetic target object 702 has
ledge 706 having a first ledge portion 706a and a second ledge
portion 706b, disposed along the length of ferromagnetic target
object 702 along the X axis. Ledge 706 has a cutout region 712
disposed between first ledge portion 706a and a second ledge
portion 706b. Ledge 706 is thus adapted to change which gear is
detected at position S3 of FIG. 4. For example, as shown in FIG. 7,
position S3 would correspond to gear G1 of FIG. 3, and state S1
would correspond to reverse R (e.g., as shown in FIG. 3).
[0068] In some embodiments, it may be desired to detect a given
gear position earlier or later than other gear positions. For
example, FIG. 8 shows another illustrative ferromagnetic target
object 802, which is similar to ferromagnetic target object 202 of
FIG. 2, but including a notch or cutout 812. Notch 812 is located
in a corner of a perimeter of a major surface 804 of ferromagnetic
target object 802, the major surface 804 disposed in the X-Y plane.
For example, notch 812 may be disposed in a corner of ferromagnetic
target object 802 opposite ledge 806 in the Y direction. For
example, notch 812 allows early detection of G6 compared to others
gears. Other locations of notch 812 may correspond to other gears
(e.g., as shown in FIG. 3).
[0069] As described, illustrative embodiments may be employed to
sense position along X and Y axes.
[0070] Referring to FIGS. 9 and 10, in which magnetic field sensors
908, 1008 with magnet 913, 1013 and magnetic field sensing elements
910a, 910b, 910c, 1010a, 1010b, 1010c can be the same as or similar
to magnetic field sensor 208 with magnet 213 and magnetic field
sensing elements 210a, 210b, 210c of FIG. 2. Other embodiments may
be employed to sense a rotation (e.g., around an X axis) and a
translation (along the X axis). For example, FIG. 9 shows
illustrative ferromagnetic target object 902, which may be a
section of a cylinder having a radius R (e.g., from a center 914 of
the cylinder). Line 918 indicates that ferromagnetic target object
902 may rotate about the X axis, and line 916 indicates that
ferromagnetic target object 902 may also move in a translation
along the X axis. Magnetic field sensor 908 may produce
differential magnetic field signals responsive to relative position
relative to ferromagnetic target object 902 similarly to the
signals shown in FIG. 4. Ferromagnetic target object 902 has sharp
edges (e.g., edge 906 and notch or cutout 912) that create sharp
variations of the differential magnetic field signal with a small
displacement.
[0071] FIG. 10 shows illustrative ferromagnetic target object 1002,
which may be a section of a cylinder having a first section 1011
having first radius R1 and a second section 1012 having a second
radius R2 (e.g., from a center 1014 of the cylinder). First section
1011 may also have a chamfered ledge 1006. Line 1018 indicates that
ferromagnetic target object 1002 may rotate about the X axis, and
line 1016 indicates that ferromagnetic target object 1002 may also
move in a translation along the X axis. In response to the varying
radius of curvature (e.g., R1 and R2) and chamfered ledge 1006,
magnetic field sensor 1008 may generate differential magnetic field
signals responsive to movement relative to ferromagnetic target
object 1002 as shown in FIG. 11.
[0072] As shown in FIG. 11, thresholds, T1 and T2 determine 3
positions (e.g., gears or groups of gears). For example, when the
differential magnetic field signal, dH, is greater than threshold
T1, gear shift lever 101 may be determined to be in a position, S1,
associated with a first given gear. For example, position S1 may
correspond to one or more forward gears. When the differential
magnetic field signal, dH, is between thresholds T1 and T2, gear
shift lever 101 may be determined to be in a position, S2,
associated with a second given gear over a position range from Y1
to Y2, which is a smaller range than that shown in FIG. 4. The
differential field is also spread on a larger displacement around
positions S2 and S3. Position S2 may correspond to neutral. When
the differential magnetic field signal, dH, is less than threshold
T2, gear shift lever 101 may be determined to be in a position, S3,
associated with a third given gear. Position S3 may correspond to
reverse.
[0073] It should be appreciated that FIG. 12 shows a flowchart
corresponding to the below contemplated technique which would be
implemented in a magnetic field sensor, e.g., 102 (FIG. 1).
Rectangular elements (typified by element 1202 in FIG. 12), herein
denoted "processing blocks," represent computer software
instructions or groups of instructions. Diamond shaped elements (of
which there are none) herein denoted "decision blocks," represent
computer software instructions, or groups of instructions, which
affect the execution of the computer software instructions
represented by the processing blocks.
[0074] Alternatively, the processing and decision blocks represent
steps performed by functionally equivalent circuits such as a
digital signal processor circuit or an application specific
integrated circuit (ASIC). The flow diagrams do not depict the
syntax of any particular programming language. Rather, the flow
diagrams illustrate the functional information one of ordinary
skill in the art requires to fabricate circuits or to generate
computer software to perform the processing required of the
particular apparatus. It should be noted that many routine program
elements, such as initialization of loops and variables and the use
of temporary variables are not shown. It will be appreciated by
those of ordinary skill in the art that unless otherwise indicated
herein, the particular sequence of blocks described is illustrative
only and can be varied without departing from the spirit of the
invention. Thus, unless otherwise stated the blocks described below
are unordered meaning that, when possible, the steps can be
performed in any convenient or desirable order.
[0075] Referring to FIG. 12, a flow diagram of illustrative process
1200 for determining a gear shift lever position is shown. At block
1202, process 1200 starts. At block 1204, in some embodiments,
magnetic field sensor 102 determines a set of magnetic field
sensing elements (e.g., signals 122) to use to generate the
differential magnetic field signal, dH. For example, as described
in regard to FIGS. 5 and 6, magnetic field sensor 102 may select
two magnetic field sensing elements having a greatest distance from
an edge of the ferromagnetic target object (e.g., magnetic field
sensing elements M2 and M3 as shown in FIG. 6). In other words,
magnetic field sensor 102 may select two magnetic field sensing
elements having a greatest distance (e.g., D.sub.1+D.sub.2 as shown
in FIGS. 5 and 6) from the ferromagnetic target object to guarantee
the largest magnetic field signal. In some embodiments, at block
1204, magnetic field sensor 102 determines weighting coefficients
for each of the magnetic field sensing elements (e.g., to weight
signals 122) used to generate the differential magnetic field
signal, dH. In some embodiments, magnetic field sensor 102 may
determine a set of magnetic field sensing elements, and also
determine weighting coefficients for the selected set of magnetic
field sensing elements.
[0076] At block 1206, the differential magnetic field signal, dH,
is generated based on selected set of magnet field sensing elements
with or without determined weighting coefficients. At block 1208,
the position of a gear shift lever (e.g., gear shift lever 101) is
determined based upon the differential magnetic field signal, dH,
generated at block 1206. Magnetic field sensor 102 outputs the
position of the gear shift lever (e.g., as output signal 136). At
block 1210, process 1200 completes. Process 1200 may be performed
each time a position of the gear shift lever is determined.
[0077] Although described herein as being employed in a gear shift
sensing system to determine a gear shift lever position (e.g., in a
vehicle gearbox), and in particular for a neutral gear sensor,
described embodiments may be employed in other applications
requiring detection of three positions in a system having two axes
of movement or translation.
[0078] Described embodiments are fully differential and employ back
bias magnets and ferromagnetic target objects. In some embodiments,
the magnet can be integrated in the package with the magnetic field
sensor. Some embodiments have no upper limit for the sensed
magnetic field level.
[0079] In described embodiments, processing system 124 may be
implemented as one or more processors. As used herein, the term
"processor" is used to describe an electronic circuit that performs
a function, an operation, or a sequence of operations. The
function, operation, or sequence of operations can be hard coded
into the electronic circuit or soft coded by way of instructions
held in a memory device. A "processor" can perform the function,
operation, or sequence of operations using digital values or using
analog signals. In some embodiments, the "processor" can be
embodied in an application specific integrated circuit (ASIC). In
some embodiments, the "processor" can be embodied in a
microprocessor with associated program memory. In some embodiments,
the "processor" can be embodied in a discrete electronic circuit.
The "processor" can be analog, digital or mixed-signal.
[0080] Illustrative embodiments may be implemented as a circuit, an
integrated circuit, a multi-chip module, a single card, or a
multi-card circuit pack. Various functions of circuit elements may
also be implemented as processing blocks in a software program.
Such software may be employed in, for example, a digital signal
processor, microcontroller, or general purpose computer. Thus,
described embodiments may be implemented in hardware, a combination
of hardware and software, software, or software in execution by one
or more processors.
[0081] Some embodiments may be implemented in the form of methods
and apparatuses for practicing those methods. Described embodiments
may also be implemented in the form of program code, for example,
stored in a storage medium, loaded into and/or executed by a
machine, or transmitted over some transmission medium or carrier,
such as over electrical wiring or cabling, through fiber optics, or
via electromagnetic radiation. A non-transitory machine-readable
medium may include but is not limited to tangible media, such as
magnetic recording media including hard drives, floppy diskettes,
and magnetic tape media, optical recording media including compact
discs (CDs) and digital versatile discs (DVDs), solid state memory
such as flash memory, hybrid magnetic and solid state memory,
non-volatile memory, volatile memory, and so forth, but does not
include a transitory signal per se. When embodied in a
non-transitory machine-readable medium, and the program code is
loaded into and executed by a machine, such as a computer, the
machine becomes an apparatus for practicing the method.
[0082] When implemented on a processing device, the program code
segments combine with the processor to provide a unique device that
operates analogously to specific logic circuits. Such processing
devices may include, for example, a general purpose microprocessor,
a digital signal processor (DSP), a reduced instruction set
computer (RISC), a complex instruction set computer (CISC), an
application specific integrated circuit (ASIC), a field
programmable gate array (FPGA), a programmable logic array (PLA), a
microcontroller, an embedded controller, a multi-core processor,
and/or others, including combinations of the above. Described
embodiments may also be implemented in the form of a bitstream or
other sequence of signal values electrically or optically
transmitted through a medium, stored magnetic-field variations in a
magnetic recording medium, etc., generated using a method and/or an
apparatus as recited in the claims.
[0083] It should be understood that the steps of the illustrative
methods and processes set forth herein are not necessarily required
to be performed in the order described, and the order of the steps
of such methods and processes should be understood to be merely
examples. Likewise, additional steps might be included in such
methods and processes, and certain steps might be omitted or
combined, in methods and processes consistent with various
embodiments.
[0084] Various elements, which are described in the context of a
single embodiment, may also be provided separately or in any
suitable subcombination. It will be further understood that various
changes in the details, materials, and arrangements of the parts
that have been described and illustrated herein may be made by
those skilled in the art without departing from the scope of the
following claims.
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